Moscow has been bombing in Syria since September 30, saying it is backing forces loyal to President Bashar al-Assad against ISIS jihadists and other “terrorist” groups.

But the U.S. and its allies involved in a separate air campaign against ISIS have accused Moscow of primarily hitting more moderate groups fighting against Assad’s regime.

Moscow said it had set up “working coordination groups” aimed at bolstering the fight against ISIS, but said the identities of those involved were being kept secret.

“Such close cooperation will allow us to unite the efforts of the government troops with other patriotic forces in Syria that used to be in the opposition and act as a united front against the common enemy — international terrorism,” the defence ministry said in a statement.

Joint training exercise

Meanwhile, the Russian and U.S. air forces held a joint training exercise in Syria on Tuesday, Russian news agencies reported, citing a general with Russia’s armed forces.

Interfax news agency also reported, citing General Andrei Kartapolov, that Russia and Israel were informing each other continually on the situation in Syrian airspace.

However, U.S. official told Reuters that a U.S. fighter aircraft and a Russian fighter aircraft conducted a communication test in skies over south central Syria on Tuesday to validate safety protocols agreed between the two countries last month.

The U.S. military official, speaking on condition of anonymity, said the two aircraft came within 5 miles (8 km) of one another. The test lasted about 3 minutes.